The CHO miRNA Transcriptome - MicroRNAs as Tools in Biopharmaceutical Production - page 56

Fig. 4.3 Transcription of miRNAs in CHO cell lines . a Heatmap illustrating mature miRNA tran-
script levels in six distinct CHO cell lines, where clusters of high, medium and low abundant
miRNAs are indicated. b Cumulative fraction plot showing log 2 fold changes in miRNA expression
for three different comparisons: CHO-K1 serum-free adapted (sf) versus serum-dependent (fcs),
DXB11 sf versus fcs and CHO-K1 sf versus DXB11 sf. Results indicate a trend towards global
down-regulation of miRNA transcription or processing in serum-free adapted CHO cell lines, but
not for control comparison of serum-free CHO-K1 to DUKXB-11. (data derived from Hackl et al.
2011 , ref. 18)

Therefore, several studies in CHO have focused to measure miRNA transcript
levels under certain conditions, in order to relate their expression to cell type, prolif-
eration, apoptosis and recombinant protein production (Table 4.1 ). In the following,
a detailed summary of the respective results will be given.

4.4 The CHO miRNome

4.4.1 Correlation of miRNA Expression with Cellular State

Quantitative analysis of next-generation sequencing data showed that the majority
of miRNAs in CHO cells exhibit low to medium expression levels (60 %) with only
some miRNAs, especially members of the let-7 family and miR-21 (Hackl et al.
2012 ), that seem to be highly abundant in CHO cells (Fig. 4.3 a). As indicated by the